1. Field of the Invention
The present invention relates generally to cordless telephony and more particularly to multiplexing time slots of two communications systems.
2. Background of the Invention
The ISM (Industrial Scientific Medical) band includes 902-928 MHz, 2.4-2.483 GHz, and 5.725-5.875 GHz frequency ranges. In the United States, the ISM band is unlicensed, which means that any of the ISM band frequency ranges can be used in a variety of applications as long as Federal (FCC) Communications Commission's part 15 rules are followed. One such application involve cordless telephones, which operates in each of the 900 MHz, 2.4 GHz, and 5.8 GHz ranges. Another application of the ISM band involves Bluetooth (BT) wireless technology, which uses the 2.4 GHz range frequencies.
BT technology is used by cellular telephones to enable communication between a cordless headset (e.g., one that can be worn on a user's head to enable “hands-free” operations) and a cellular telephone (e.g., one that can be attached to the user's belt). In such an application, a BT transceiver is housed within each of the cordless headset and the cellular telephone. Since BT transceivers and the cellular handset operate at different frequency bands, no significant interference is experienced.
Similar utility of the BT technology has not been made in cordless telephones. This is because incorporation of the BT technology in the cordless telephone sector would likely cause unacceptable interference in the 2.4 GHz ISM band. For example, in a situation in which a BT transceiver is located in a cordless handset that already has a conventional 2.4 GHz cordless telephone transceiver, significant interference can be expected. Due to the significant interference, an acceptable communications session between a BT headset and the cordless handset may not be achievable. Currently, there is no known solution that would enable a 2.4 GHz cordless telephone to communicate with a BT headset without interference.
U.S. Pat. No. 5,627,823 discloses a wire-free telecommunications system having multiple base stations and mobile units, each of which has a circuit arrangement to which a controlling program is assigned. The system includes radio links at predetermined frequencies and in multiple time slots in time-division multiplex channels. The controlling program uses only a subset of the time slots which do not follow one another directly which are predetermined for the radio links. In short, technology disclosed in this patent is related to time synchronization, but it is not related to multiplexing slots for two different/independent communications systems.
U.S. Pat. No. 5,625,888 discloses a process for combining transmitting/receiving devices of a cordless communications system to form a communicating unit. The disclosed technology is based upon coordination between two units by sending messages back and forth to achieve synchronization.